Objectives: To define the rate of positive surgical margins (PSMs) and analyze the outcome of patients with PSMs. The outcome and proper management of patients with positive PSMs during nephron sparing surgery (NSS) are questionable. In this study we define the clinical outcomes of PSMs at NSS and suggest management. Methods: Clinical records of 114 renal units who underwent open NSS for a renal mass between May 1995 and September 2005 were reviewed. Results: PSMs were suspected on frozen section in 17 of 114 renal units (15%). Tumors with suspected PSMs at frozen section were smaller (2.9 ± 1.6) in comparison to those with negative surgical margins (3.4 ± 1.8 cm) (P = .001). Nine of 17 (53%) cases underwent total nephrectomy (5 immediately, 4 delayed). In 4 (24%), immediate re-excision of the renal crater was performed. A total of 4 (24%) that were followed up clinically were with no evidence of disease. Therefore, in 13 of 17 (77%) cases, the presence of tumor cells at the remaining side of the kidney could be evaluated histologically. In 2 cases from the immediate response group, tumor cells were found in the side opposite to the resection. There was no residual tumor in any case subjected to delayed nephrectomy. At median follow-up of 71 months, 15 of 17 patients are alive and with no evidence of disease. Two patients died because of unrelated causes. The overall 5-year survival rate is 98.2% and there is no cancer-specific mortality. Conclusions: The true PSM rate is in the range of 1.75%-5.26%. No disease progression or deaths attributable to renal cell carcinoma were associated with PSMs. Total nephrectomy should be avoided as a response to PSMs.